1. Field of the Invention
This invention is directed to an alignment mark used to align a mask to form a feature at a desired position on a substrate. The invention is also directed to a method for making the mark.
2. Description of the Related Art
In the formation of a magneto-resistive (MR) thin-film head device, the head device is integrated into a substrate so that it extends across a dice line. Upon dicing the side edge of the substrate, the head device is exposed in the substrate's side edge. The substrate's side edge is polished and subjected to selective removal of portions of the substrate and device through ion milling or reactive ion etching, for example, to form a relatively narrow write gap bridge. With its narrow width, the write gap bridge can be used to write correspondingly narrow data tracks on a magnetic storage device such as a hard disk drive. The narrow width of the data tracks allows the tracks to be more closely spaced to increase data density of a magnetic storage device with which the head device is used.
The selective removal of portions of the substrate and head device to form the write gap bridge must be performed with high accuracy so that the write gap is properly positioned with respect to the portion of the MR layer used to read data. To perform the selective removal of material in the proper locations, a resist layer is formed and patterned to selectively expose the appropriate portions of the substrate and head device. The current practice to align the mask used to form the resist layer for ion milling, is to use a specific component of the head device as a positional reference for alignment. However, the ideal reference component for alignment in a MR thin film head is the MR contact layer, which is extremely thin in width, usually from 0.1 to 0.2 microns. Accordingly, the alignment system has great difficulty detecting the head device's reference component, if it is able to do so at all. Furthermore, by aligning to a component of the head device, the alignment system must be moved relative to the substrate before transfer of the mask pattern to the resist layer by exposure, thus introducing inaccuracy in the alignment of the mask used to form the feature. It would be desirable to overcome these disadvantages of previous devices and techniques for aligning features on the side surface of a substrate.